Snap hooks in the safety and lifting industries take a variety of different forms and have an equally wide number of different applications. Such applications include use in fall arrest systems and in the lifting of heavy objects by means of a crane or other lifting devices.
The safe lifting of heavy objects and the prevention of falls is of primary importance on construction sites and in situations where individuals may be working at heights, around areas of excavation, or where a personal fall or the dropping of an object that is being lifted could result in property damage, serious injury or death. Furthermore, in many jurisdictions the employment of a fall arrest system to prevent personal injury is not only desirable, but is a statutory requirement. Commonly fall arrest systems involve the placement of a harness or belt around an individual and then the subsequent use of a rope, cable or strap to secure the harness or belt, and hence the individual, to a solid structure. For example, individuals working on bridges, towers or tall buildings will commonly wear belts or safety harnesses that include a lifeline typically comprised of a rope or strap having its free end secured to the structure upon which they are working. In the logging industry, and in situations where individuals are working on utility poles, a worker is often fitted with a safety belt or harness having a rope or strap that is connected to the belt or harness at one end, is passed around the tree or pole, and that has its free end connected to an opposite side of the belt. At least one end of the rope or strap is usually fitted with a snap hook to enable it to be readily engaged and disengaged from the safety belt or support structure.
In theory, should a worker slip or fall while wearing a safety belt or a harness that is securely attached by way of a lifeline to a solid structure, the worker will only be allowed to fall a short distance after which his decent will be stopped and he will be suspended until he can regain his balance or be rescued. In practice the safety harness and fall arrest systems currently in use do not always function as designed and accidents, injuries and fatalities sometimes occur. One type of failure that can have disastrous results is a failure of the hook used on the end of a lifeline. Similarly, the failure of a hook used in the lifting of heavy objects can be equally dangerous.
Due to their convenience and ease of use, snap hooks having a gate keeper that encloses the hook bowl are probably the most widely used method to secure the end of a lifeline to an object. For the same reasons such hooks are commonly used in a extremely wide variety of other applications, including for the lifting of objects. Unfortunately, simple snap hooks can become unintentionally opened through the application of a force against their gate keeper. As a result, others have proposed and developed a variety of different locking mechanisms that assist in maintaining the gate keeper in a closed position (for example, see U.S. Pat. No. 4,062,092 dated Dec. 13, 1997; U.S. Pat. No. 4,122,585 dated Oct. 31, 1978; U.S. Pat. No. 5,257,441 dated Nov. 2, 1993; U.S. Pat. No. 5,579,564 dated Dec. 3, 1996; and U.S. Pat. No. 5,896,630 dated Apr. 27, 1999.) While such locking mechanisms have reduced the likelihood of an unintentional opening of the hook, they are generally limited in their ability to prevent the gate keeper from becoming dislodged from the end of the hook bowl or bill through the application of forces or loads that may be applied directly to the gate keeper.
For ease of use, many gate keepers require the application of a single force to either the keeper or its lock in order to “open” the hook. In some instances others have designed keeper and lock structures that require the application of two discrete forces to open the hook, one force directed to the lock and one force directed to the keeper. Nevertheless, even in such cases it has been found that situations as innocuous as leaning against a hook that is bearing against a solid surface can be sufficient to cause an accidental disengagement of the gate keeper from the hook's bill. Where that occurs the hook may unintentionally become dislodged and present a significant threat to the safety of personal and equipment.